Typhus is an infectious disease that is spread by lice, fleas, and insects. The name comes from the Greek typhos, meaning smoky or lazy, describing the state of mind of those affected with typhus. A number of different illnesses are called "typhus," all of them caused by one of the bacteria in the family Rickettsiae. Each illness occurs when the bacteria is passed to a human through contact with an infected insect. Rickettsia is endemic in rodent hosts, including mice and rats, and spreads to humans through mites, fleas and body lice. There are four main types of typhus epidemic typhus, Brill-Zinsser disease, endemic or murine typhus, and scrub typhus.
Epidemic typhus, which is occasionally called jail fever or louse-borne typhus, is caused by Rickettsia prowazekii, which is carried by body lice. Once the lice feed on a human, they may simultaneously defecate. As the person scratches the bite, the feces (which carrys the bacteria) are scratched into the wound. Body lice are common in areas in which people live in overcrowded, filthy conditions, with few chances to wash themselves or their clothing. Because of this fact, this form of typhus arises simultaneously in large numbers of individuals living within the same community. This type of typhus occurs when cold weather, poverty, war, and other disasters result in close living conditions that encourage the preservation of a population of lice living among humans.
Brill-Zinsser disease is a reactivation of an past infection with epidemic typhus. It affects people years after they have fully recovered from epidemic typhus. While something causes a weakening of their immune system (like aging, surgery, illness), the bacteria can gain hold again, causing illness. This illness tends to be extremely mild.
Endemic typhus is carried by fleas. When a flea lands on a human, it may defecate as it feeds. When the person scratches the itchy spot somewhere the flea was feeding, the bacteria-laden feces are scratched...